The European court of human rights in Strasbourg is already the most important international human rights tribunal in the world. It hears cases from the 47 (EU and non-EU) member states of the Council of Europe, which have more than 800 million people.

Last month talks began that will lead to the EU becoming the 48th party to the European convention on human rights, with its own judge joining the court. It will be possible to take a case to the court (eg, Ahmed v European Union, instead of Ahmed v 27 EU member states) claiming that part of EU law (eg, a regulation or directive) violates a human right protected by the convention, after exhausting remedies under EU law (eg, a reference to the EU court of justice in Luxembourg).

Individuals complaining about EU law will join those complaining about national law in the (long) queue in Strasbourg. There, they will often be disappointed by the court's judgments, because they see it as an all-powerful "saviour", imposing the highest possible standard. Yet the court frequently takes the opposite approach. It looks for a minimum standard with regard to a particular issue, based on evidence of an emerging legal, political or social consensus across 47 European countries.

A good example is equal access to legal marriage for same-sex couples. On 24 June, in Schalk and Kopf v Austria, the court decided that the convention does not yet require equal access. If the court applied human rights principles strictly, it would have found a violation. The court requires particularly serious reasons to justify legal distinctions based on sexual orientation, and has said that a couple seeking to marry need not have capacity to procreate, or be of different sexes. But this is where "European consensus" constrains the court's application of human rights principles: only seven of 47 European countries allow same-sex couples to marry. (Another 13 provide registered partnership.)

Is this consensus-based approach a strength or a weakness of the court? Although I found it frustrating at first, I consider it a strength. The court looks for consensus because its judgments are binding. When it takes a stand on a particular human rights issue, it expects 47 European countries to follow, sooner or later. Expulsion from the Council of Europe is the ultimate sanction for failure to comply with a judgment of the court. If the court appeared to force the views of a small minority of countries on all 47, it would risk a political backlash, which could cause some governments to threaten to leave the convention system. As a result, the ability of the court to assist, with regard to a particular issue in a particular country, depends on the state of "European consensus".

The UK lagged far behind most of Europe in lesbian, gay, bisexual and transgender (LGBT) human rights until 2002. The court (and the former commission) found violations in Dudgeon (1981, criminalisation in Northern Ireland), Sutherland (1997, age of consent), Smith and Grady (1999, armed forces), ADT (2000, group sexual activity), and Christine Goodwin (2002, change of birth certificate and different-sex marriage for transsexual woman).

Now, apart from the "M-word" (marriage) the UK leads Europe in the area of LGBT human rights. At some point, the court will require all 47 European countries to adopt the equality for same-sex couples that the UK has introduced voluntarily since 2003 (civil partnership, joint adoption, parental rights after donor insemination in the UK or surrogacy abroad).

"European consensus" serves to anchor the court in legal, political and social reality on the ground. By contrast, United Nations human rights law often loses all contact with Earth, and floats off into the stratosphere. Laudable pronouncements about human rights are made, but they are not binding on governments, and there are no sanctions for non-compliance, especially not expulsion from the UN.

The closest we have to a world court of human rights is the UN human rights committee in New York and Geneva. But it is a committee, not a court, and issues non-binding "views", rather than binding judgments. If the price of binding human rights law is patience, while consensus builds at the national level, I am happy to pay it.

Robert Wintemute is a professor of human rights law at King's College London